Replacing a window involves a few critical steps to ensure a perfect fit. First, identify the window stop molding on the inside of the window frame. This molding is the piece that butts directly against the window itself. Carefully remove it to expose the window opening.

Next, measure the dimensions of the exposed opening. To ensure a proper fit, subtract ½ inch from both the width and height of the opening. This adjustment will leave a ¼ inch gap all around the new window, allowing for easy installation and proper sealing.

When selecting your new window, choose a size that best fits these adjusted dimensions. If needed, you can modify some of the surrounding wood molding to accommodate different styles, such as converting a casement window to a slider or a wider double-hung window.

With these steps, you'll ensure your new window fits perfectly and functions smoothly.